As disk type magnetic recording mediums used for still video, computers, etc., magnetic recording mediums have been hitherto used in which a magnetic layer comprising ferromagnetic alloy powder dispersed in a binder is coated on a non-magnetic support. As the magnetic recording mediums of such types are made higher in density and higher in S/N ratio, it has been recently attempted to make finer the particles of magnetic materials. As the particles are made finer, however, the abrasive properties of magnetic materials are lowered to bring about problems of head clogging and a lowering of durability. In addition, the ferromagnetic alloy powder has originally not so good dispersibility in a binder, and hence in actual circumstances it is difficult to obtain electromagnetic conversion characteristics as expected.
As a countermeasure to prevent the lowering of durability, the head clogging, etc. as stated above, it has been hitherto proposed to add an abrasive such as Al.sub.2 O.sub.3, SiC or Cr.sub.2 O.sub.3 in a magnetic layer. If, however, such an abrasive is added in a large quantity, a magnetic recording medium involves a deterioration of the degree of packing of magnetic powder or a deterioration of the dispersibility thereof, bringing about the problem of a lowering of electromagnetic conversion characteristics because of the deterioration of surface properties.
If the abrasive is added in a smaller amount so that the surface properties can be improved, the electromagnetic conversion characteristics can be improved but no sufficient abrasive properties can be obtained, making it impossible to satisfactorily prevent the lowering of durability, the head clogging, etc.
On the other hand, Cr.sub.2 O.sub.3 particles originally take a time for their dispersion. When a magnetic coating composition is prepared taking account of the dispersion thereof, they not only can be dispersed with a poor efficiency but also may cause a break of crystals of magnetic powder, so that there is a possibility of the deterioration of magnetic characteristics. Moreover, if Cr.sub.2 O.sub.3 particles are added as they are, the surface of a magnetic layer may become rough because of their poor dispersion or the Cr.sub.2 O.sub.3 particles themselves may fall off to cause dropouts or the like.